BOSTON — Republican Mitt Romney, who last week struggled with his responses to a major ­foreign policy crisis in the Middle East, will turn his focus back to the economy with a new offensive aimed at recharging a campaign that even some allies believe he is losing.

The Obama campaign, also sobered by the violent deaths of U.S. diplomats in Libya, seems willing to join Romney in a debate about the economy instead.

The GOP nominee, in speeches and television advertisements this week, will roll out more details about his plans to help the middle class by creating jobs, cutting the deficit and developing more domestic energy resources, advisers said. The specifics are designed to give voters a clearer sense of what Romney would do as president.

The Republican blowback to Romney’s handling of the Libya crisis follows widespread disappointment in the party that the campaign flubbed his nominating convention in Tampa by not delivering a coherent message or presenting the nominee’s agenda in concrete terms.

One top donor to the Romney campaign said that the convention did not present Republicans as successful and that the messaging at the Democratic convention in Charlotte was much stronger and more effective. Several donors said they did not understand why Romney adopted such an abrasive tone in his acceptance speech, instead of dispassionately making a case for his candidacy.

On Sunday night, the campaign was dealing with more fallout from the convention after Politico published a story describing a campaign operation in disarray, with many accusatory fingers pointed at chief strategist Stuart Stevens, particularly for the perceived failings of the convention speech.

Romney is determined to reshape a congealing narrative that he has fallen behind Obama and will spend the next 21/2 weeks before the first presidential debate articulating more-concrete details of his five-step economic plan, according to campaign advisers.

The strategy shift indicates that the Romney campaign is heeding the advice of senior Republicans, who for weeks have publicly urged the Romney operation to combine its indictments of Obama’s record with a stronger rationale for a Romney presidency.

“I think people are waiting to get a little more information, and the key for us is to make sure that voters know why voting for Romney will result in a change and an improved economy,” Ed Gillespie, a senior adviser to Romney, said in an interview. “We’re going to keep pounding away on a future-oriented campaign about why the next four years will be better under Mitt Romney than under President Obama.”

The Romney campaign has prepared a series of ads, to air in battleground states, arguing that Romney’s plan would create 12 million jobs. Aides said the ads will highlight his trade policies to crack down on China, his plans to help small businesses grow and his specific plan to cut the spiraling federal deficit.

The national debt will be a key focus early this week. Romney and his running mate, Rep. Paul Ryan (Wis.), will highlight the debt burden that mothers and grandmothers will pass on to their children and grandchildren — an issue advisers think can help Romney close the gap with Obama among female voters. The campaign also plans to stage a ticking electronic debt clock at campaign rallies, an aide said.

Romney touched on the debt in a podcast released to supporters over the weekend, saying that Obama was “passively allowing us to go over a fiscal cliff.” Romney’s plan calls for capping federal spending at below 20 percent of the economy — cuts he says he would achieve in part by consolidating federal agencies and transferring some government programs to the states.

Obama has argued that Romney’s proposed cuts would devastate the middle class, and aides said the president will engage Romney head-on in that debate this week. Obama kicks off a busy campaign week by returning to the critical battleground of Ohio, with appearances scheduled Monday in Cincinnati and Columbus.

As he has done repeatedly on the trail, Obama will warn of the consequences of Romney’s plans to cut taxes for the wealthiest Americans and tout his administration’s bailout of the U.S. auto industry three years ago, aides said. They cast Romney as a flailing candidate trying repeatedly to reinvent himself without success.

“Mitt Romney has already laid out his five-point plan and it is chock full of bad news for the middle class,” Obama campaign spokeswoman Jen Psaki said Sunday in an e-mail. She listed repealing changes to Wall Street and Obama’s health-care overhaul among the initiatives Romney would pursue if elected.

Both candidates have a heavy load of fundraising ahead as they furiously try to amass cash to finance the expensive advertising blitz in the final weeks before Election Day. Obama will raise money in New York at an event headlined by music power couple Jay-Z and Beyoncé, while Romney will be raising money in California, Texas and Florida.

The two will face off in dueling appearances in Miami at a forum sponsored by Univision, the ­Spanish-language television network. Romney will speak at the forum on Wednesday, a day before Obama, and both candidates will answer questions.

Romney has struggled to make inroads with Latino voters but will make an aggressive push this week, both at the Miami forum and in a speech Monday to the U.S. Hispanic Chamber of Commerce in Los Angeles. In each case, aides said Romney will talk about his plans to help small-business owners and why he thinks Obama’s health-care overhaul hurts Hispanic entrepreneurs.

In the 2008 campaign, Obama won 67 percent of the Latino vote, and the president has heavily courted them this year, touting his recent directive to stop deporting some illegal immigrants who were brought to the country as children and have gone on to be productive and otherwise law-abiding residents.

Although polls show him leading Romney by solid margins among Latinos, Obama’s pollsters say he needs to extend his margin from four years ago to make up for potential losses among other voting demographics.

Overall, the spate of recent polls spell trouble for the Romney effort. Although the race remains close nationally in head-to-head matchups, Romney is losing ground in several key battleground states, particularly Ohio, that are essential to a winning electoral calculus.

Romney’s selection of Ryan seems to have helped him expand the battlefield to put Wisconsin in play. Both campaigns are spending money there, and Obama is scheduled to campaign on Saturday in Milwaukee, the president’s first stop in Wisconsin since Ryan joined the GOP ticket.

Yet a pair of Democratic-leaning states the Republicans had hoped to contest — Michigan and Pennsylvania — seem to be slipping out of reach for Romney. In Pennsylvania, for instance, Obama opened an 11-point lead over Romney, 50 percent to 39 percent, in a Philadelphia Inquirer poll released Saturday.

Here in Boston, however, Romney’s strategists insist that Obama’s bounce in polling is little more than an ephemeral “sugar high” coming out of the Democratic National Convention. They insist they can win and are aggressively contesting the conventional wisdom that Romney is on a downward trajectory.

In interviews, some Romney advisers privately spewed off a list of polls, nationally and in key states including Florida and Colorado, showing Romney in contention.

Key to his winning will be the first debate, Oct. 3 in Denver. Just like Obama, who has been studying Romney’s record and preparing to defend his own, Romney has held numerous sessions with top advisers to prepare for the debates.

Romney held no public campaign appearances this past weekend, but he told reporters that he spent much of Saturday “studying.” On Sunday morning, before flying to Los Angeles, Romney held a debate-prep session near his home in Belmont, Mass.

Sen. Rob Portman of Ohio has played Obama in the mock rehearsals, and when asked on Friday night whether Romney’s debating skills were improving, Portman said: “He’s doing great.”